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\psarc(1,1){0.3}{0}{35}
\rput[r](-0.1,1){$N_{i-1}$}
\rput[r](-0.1,4){$N_{i}$}
\rput[t](1,-0.1){$l_{i-1}$}
\rput[t](5,-0.1){$l_{i}$}
\rput[l](1.4,1.2){$\alpha$}
\rput[l](6,3){\color{royalblue1} $\tg(\alpha) = \dfrac{N_i-N_{i-1}}{l_i-l_{i-1}}$}
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\rput[r](-0.1,3){$n/2$}
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\rput[l](6,2){\color{coral}$\tg(\alpha) = \dfrac{n/2-N_{i-1}}{Me-l_{i-1}}$}
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